1. Field of the Invention
The present invention relates to a Field Emission Display (FED), and more particularly, to a FED with an electron emission structure capable of improving the focusing characteristics of electron beams as well as uniformity of current density distribution.
2. Description of the Related Art
A conventional display that is an essential part of an information transfer medium has been commonly used as a PC monitor or a TV screen. Displays are largely classified into Cathode Ray Tubes (CRTs) based on high-speed thermal electron emission and Flat Panel Displays (FPDs) showing rapid growth, such as Liquid Crystal Displays (LCDs), Plasma Display Panels (PDPs), and Field Emission Displays (FEDs).
In an FED, emitters arranged on a cathode electrode at regular intervals emit electrons when a strong electric field is applied from a gate electrode. The electrons from the emitters strike and excite a phosphor material formed on an anode electrode, causing it to emit light. The image quality characteristics of an FED in which electrons emitted from a cold cathode are focused on a screen to create an image are significantly affected by the material or structure of an emitter as an electron source.
At an early stage of development, an FED used a metal tip (micro-tip) made of molybdenum (Mo) as an emitter. However, the FED with a metal-tip emitter requires the formation of ultra-microscopic holes to arrange emitters and Mo deposition for formation of a uniform metal micro-tip across the entire screen surface. Thus, the FED requires a complicated fabrication process, a highly sophisticated technology, and the use of expensive equipment, resulting in high manufacturing costs. Thus, the FED with a metal-tip emitter has a restriction on increasing its screen size.
To facilitate electron emission at low driving voltage and simplify the manufacturing process, the FED industry is conducting research into a technology for the fabrication of a planar emitter.
According to a current technology, a carbon-based material such as graphite, diamond, Diamond like Carbon (DLC), C60 (Fulleren), or Carbon NanoTubes (CNTs) are suitable for forming a planar emitter. In particular, the CNTs emerge as the most ideal material for forming an emitter of a FED since they allow easy electron emission at low driving voltage.
A FED typically has a triode structure with a cathode electrode, an anode electrode, and a gate electrode. That is, the FED includes cathode electrodes and gate electrodes formed on a rear substrate, the anode electrode formed on a front substrate, and phosphor layers consisting of Red (R), Green (G), and Blue (B) phosphors and black matrices for improving contrast formed on the anode electrode. The rear and front substrates and are spaced apart by a spacer located therebetween. A method of fabricating the FED involves forming the cathode electrodes on the rear surface on which emitters will be arranged, sequentially forming an insulating layer with microscopic apertures and the gate electrodes on the cathode electrodes, and arranging emitters on the cathode electrodes within the apertures 15.
However, the triode-type FED suffers degradation in color purity and difficulty in realizing a sharp image because electron beams emitted from the emitter toward the phosphor layers diverge due to the positive voltage (several tens of volts) supplied to the gate electrode such that not only phosphors at a desired pixel but also adjacent phosphors emit light.
To prevent divergence of an electron beam, a FED with a gate focusing electrode for focusing an electron beam on a gate electrode has been proposed. Such a FED includes a gate focusing electrode that is formed on a second insulating layer deposited on a gate electrode and controls the trajectory of an electron beam.
However, the FED with the gate focusing electrode can suffer poor focusing due to changes in anode voltage and gate focusing voltage. A beam profile becomes uneven as a gate focusing voltage varies, resulting in poor focusing. The poor focusing causes electrons to excite a phosphor layer other than the target phosphor layer, thereby degrading pixel uniformity.